In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, a hot process gas is generated, such process gas containing, among other components, carbon dioxide CO2.
With increasing environmental demands various processes for removing carbon dioxide from the process gas have been developed. One example of such a process is the so called oxy-fuel process. In an oxy-fuel process a fuel, such as one of the fuels mentioned above, is combusted in the presence of a nitrogen-lean gas. In the oxy-fuel combustion process a carbon dioxide rich flue gas is produced, which can be disposed of in order to reduce the emission of carbon dioxide. The carbon dioxide rich flue gases may also comprise contaminating gases, for example NOx gases. These contaminants shall also be removed. There are different methods available for removal of the nitrogen oxides from a gas flow, for example the NOx gases can be removed by using GPU offgas or by using a so called DeNOx unit, acting by catalytic reduction.
U.S. Pat. No. 6,146,605 describes methods like selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), and combinations thereof, for reduction of NOx in flue gases. The NOx gases are herein removed by using ammonia (NH3) as a reducing agent. This system is not connected to a system for regeneration of desiccants.
In U.S. Pat. No. 4,533,365 the gas containing NOx gases is separated by a molecular sieve and recycled into the system.
In previous used systems for regeneration of drying desiccants contaminants, like NOx gases, are coadsorbed. When the desiccants then were regenerated the NOx gases were also released, which resulted in disadvantageous concentration peaks of NOx in the regeneration offgas.
Therefore there is a need to solve the problem to avoid emitting or substantially avoid emitting NOx when regeneration of desiccants.